The effects of international migration on the epidemiology of tuberculosis, 2011-2021: a secondary analysis of national surveillance data

Abstract

Title: The effects of international migration on the epidemiology of tuberculosis, 2011-2021: a secondary analysis of national surveillance data Author: Sarah Jackson Introduction: Tuberculosis (TB) remains a global public health threat that was responsible for 1.3 million deaths in 2022 alone. Ireland became a low TB incidence country in 2010 and has experienced a steady decline in crude incidence rates (CIRs) to less than 5 per 100,000 during). While CIRs in the Irish-born have remained below six per 100,000 population since 2011, CIRs in the foreign-born population have been up to 13 times higher). Given increasing global migration trends, migrants remain a key population for TB prevention and care activities and require a deeper understanding of the epidemiologic patterns among native-born and foreign-born TB patients. Aim: This thesis aims to examine the effect of international migration on the epidemiology of TB in low to medium incidence countries to inform global prevention and control policies, by conducting a systematic review of the published literature and by analysing Irish TB surveillance data from 2011-2021 to compare and contrast the epidemiology of TB among Irish-born cases and migrant cases. Methods: A systematic review comparing key epidemiological indicators among migrant and non-migrant TB cases was done to inform the subsequent analysis of the Irish TB surveillance dataset. Differences in the epidemiology of TB in native-born and foreign-born populations were analysed within the Irish context, and an in-depth analysis of migrant-TB patient profiles was provided using both descriptive and analytical epidemiological methods. Effects of cessation of universal BCG vaccination on the epidemiology of paediatric TB was examined using descriptive epidemiological methods. Factors associated with TB treatment success were explored using multivariable logistic regression and random forest analyses. Results: 1) The systematic review identified significant differences among migrants from high incidence countries, and non-migrants in the overall proportions of MDR-TB cases, HIV co-infected cases, clustered cases and successfully treated cases. 2) Data from 3,364 TB cases notified in Ireland between 2011 and 2021 showed that differences in the TB patient profile were observed not only among migrants compared to Irish-born cases, but also between the migrant subgroups studied. Although a significantly declining temporal trend in crude incidence rates was still present for the latter period of the study (2017-2021) in total cases and Irish-born cases, the declining trend was no longer significant among migrant cases. Migrant TB patient characteristics differed according to the incidence level in the origin-country and according to the interval between arrival and notification as a TB case. 3) Interruption of the previously declining temporal trend in the age-specific incidence rates among 0-6 year olds during a period of universal vaccination may be an early warning of a future increase of paediatric TB cases. Eight of the 19 children notified since vaccination ceased would have been eligible to receive BCG under the current selective strategy. 4) Consistently lower odds of TB treatment success among cases infected with a drug-resistant strain of M. tuberculosis were found across all three populations examined these being, total cases, migrant cases and Irish-born cases. Conclusions: This study reported key differences between Irish-born and migrant TB cases in Ireland which can be used to tailor TB prevention and control strategies, as well as inform TB care services. Coupled with interruptions to previously declining trends among migrant TB cases and among paediatric cases, this indicates that TB prevention and care interventions to support migrant health are urgently needed alongside the pressing need for improved data quality and completeness.